Continuous casting apparatus

ABSTRACT

This specification relates to apparatus for continuous casting of molten metal. The apparatus comprises a hollow chilled mold assembly connected to a reservoir for molten metal via an orifice plate assembly. The orifice plate assembly has a perimeter at least equal to the perimeter to the hollow of he mold and is positioned between and contiguous to the chilled mold and the reservoir. The orifice plate assembly has a passageway therein for flow of molten metal from the reservoir into the mold. A substantially heat conductive segment is provided in the orifice plate and is positioned so as to permit heat flow therethrough into a perimetrical section of the mold hollow. Due to the heat flow, solidification of the embryo shell of metal being cast in the mold adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced.

United States Patent [73} Assignee Kaiser Aluminum & Chemical Corporation Oakland, Calif.

[54] CONTINUOUS CASTING APPARATUS 3,212,142 10/1965 Moritz 164/89 3,286,309 11/1966 Brondyke et. al.... 164/73 3,327,768 6/1967 Craig et. al. 164/281 Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel AtI0rneys-James E. Toomey, Paul E. Calrow and Harold L.

Jenkins ABSTRACT: This specification relates to apparatus for continuous casting of molten metal. The apparatus comprises a hollow chilled mold assembly connected to a reservoir for molten metal via an orifice plate assembly. The orifice plate assembly has a perimeter at least equal to the perimeter to the hollow of he mold and is positioned between and contiguous to the chilled mold and the reservoir. The orifice plate assembly has a passageway therein for flow of molten metal from the reservoir into the mold. A substantially heat conductive segment is provided in the orifice plate and is positioned so as to permit heat flow therethrough into a perimetrical section of the mold hollow. Due to the heat flow, solidification of the embryo shell of metal being cast in the mold adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced.

PATENTEDJULZOIH?! 3,593,778

SHEET 1 OF 2 FIG. I.

INVENTOR,

JOHN J, FOYE BY mww ATTQRNEY (IONTHNUOUS CASTING APPARATUS BACKGROUND OF THE INVENTION In the so-called continuous casting of metal, or direct chill method of casting as it is sometimes referred to, in either the vertical or horizontal position, the casting is accomplished by feeding molten metal into the inlet end of a short drastically chilled mold from a reservoir via an orifice plate having a passageway therethrough. It is drawn from the outlet end of the mold as it solidifies. A hollowed shell of metal forms within the drastically chilled mold which is strong enough to contain a liquid core of molten metal which is solidified by subsequent cooling, usually effected by spraying a liquid coolant such as water directly against the ingot wall as it emerges from the mold. The metal is solidified and continuously withdrawn from the mold. The emerging ingot is then conveniently cut to desired length without interrupting the casting operation, the duration of a casting run depending only upon the molten metal supply.

Although the mechanism of solidification is not known, it is thought that solidification of metal occurs on the meniscus or on a thin film of lubricant at the mold surface close to the meniscus thereby avoiding direct contact between liquid metal and the chilled mold surface. Ideally, the liquid metal solidifies on the lubricant film or on the meniscus a short distance from the mold wall. An ingot formed in this manner has a good surface. It is known to those skilled in the art that casting rates in this type of apparatus are related to alloy composition, ingot configuration and size. The greater the section thickness, the lower the cast rate. Ingot surface smoothness and uniformity become less as sectional thickness increases. These conditions and the resultant types of surface roughnesses take a variety of forms. Horizontally cast large diameter ingots are usually cold folded or have a pitted surface condition called "worm holes." Vertically cast ingots most frequently display a sweated (rebleed) surface. As used herein the term cold shut" shall be used generically to describe all of these conditions. The exact causes of cold shuts are not completely understood but a good discussion of the generally accepted theory may be found in US. Pat. No. 3,327,768 and No. 3,329,200.

As discussed therein, alloying constituents exert a profound effect on casting rates. The more complex, crack sensitive alloys are of necessity cast at lower rates than the softer alloys and their surfaces are correspondingly more heavily cold folded and rough. In effect, low casting rates, if necessary because of ingot size, alloy, or equipment design, have proven to be a primary cause of poor ingot surfaces. The mechanism of the phenomena responsible for the surface defects is thought to be firstly, the result of a solidified meniscus around the molten metal top of the ingot previous to the arrival of the additional molten metal. Thus, cold shut frequencies are closely related to the surface tension of the liquid metal. Elimination of the oxidizing medium, air, lessens the forming of oxide film thereby preventing a seeming increase in surface tension. The cold shuts are further aggravated by low casting rates, which allow solidification of the surface zone (embryo shell) to occur upwardly toward the mold entry immediately adjacent to the orifice plate at a rate greater than that of the ingot withdrawal from the mold. Another factor, particularly with respect to surface rebleed and sweating or exudation is shrinkage in the solid state above the solidus line. This results in the development of a gap between the mold wall and the forming embryo shell of the ingot. The liquid metal moves into this gap through the ingot surface under the influence of the hydrostatic pressure of the liquid metal.

Surface imperfections are undesirable and costly because they require the solid product to be scalped to have the surface imperfections removed and deeper cracks of course require more severe scalping. This is necessary even though the solid product is subsequently wrought as by rolling, forging or extrusion because surface imperfections in most metalscarry through to the wrought forms of the product.

In the past, various solutions to these problems have been proposed. The solution most commonly employed is to direct the flow of hot metal through the orifice plate against the mold wall so that the temperature of the metal adjacent the mold wall will be approximately the temperature of the incoming metal. Orifice plates having perforations in various shapes to direct the flow of metal in the mold as well as various types of inserts in and between the mold and] the orifice plate have been employed for this purpose. However, as the casting rate changes, the flow rate against the mold wall changes and the temperature of the metal at the meniscus changes leading to the aforementioned difficulties.

SUMMARY OF THE INVENTION It is an advantage of the instant invention, that the formation of cold folds, rebleeds, worm holes, and other surface blemishes and defects, all referred to generally herein as cold shuts are minimized by providing a superheated mold closure that will retard the upper solidification of the embryo shell.

The apparatus includes a hollow chilled mold assembly and a reservoir for molten metal. This may be either a horizontal or vertical casting assembly. An orifice plate assembly having a perimeter at least equal to the perimeter of the hollow of the mold is positioned between and contiguous to the chilled mold and the reservoir. The orifice plate assembly has a passageway therein for flow of molten metal from the reservoir into the mold. A substantially heat conductive segment is positioned in the orifice plate so as to permit heat flow therethrough into a perimetrical section of the mold hollow. In this way, solidification of the embryo shell of metal being cast in the mold adjacent the orifice plate is retarded and the formation of cold shuts in the metal is reduced. The superheat of the incoming molten alloy on both sides of the orifice plate, because of the heat conductive segment therein, is sufficient to maintain the temperature of the heat conductive segment above the melting point of the alloy being cast. Molten metal passing through the passageway or orifice of the orifice plate retains sufficient heat upon arrival at the mold wall orifice plate junction line, because of the heat conductive segment positioned in the orifice plate, to prevent solidification of the embryo shell occurring at a rate greater than that of ingot withdrawal. As a result, the forming ingot has a completely molten metal top to the full diameter of the mold bore or hollow. The ingot embryo shell then builds up or is supplied from a molten metal meniscus source rather than from a meniscus source that is alternately solid and liquid.

Advantageously, the mold assembly will include a substantially heat insulating section positioned so as to thermally insulate the heat conductive segment from the chilled mold. This is desired to prevent the heat in the heat conductive segment from being extracted by the chilled mold which would tend to defeat the purpose of the invention. Desirably, a stream of mold lubricant can also serve as the heat insulating section to thermally insulate the heat conductive segment from the chilled mold.

It is also desirable that the heat conductive segment be made of a material and so proportioned that the temperature drop across the orifice plate is not more than about one-half of the temperature in degrees Fahrenheit of the molten metal in the reservoir above its solidification temperature. In other words, the molten metal should not lose more than one-half of its superheat in passing through the orifice or passageway in the orifice plate. Preferably, the heat conductive segment is made of a material and so proportioned that the temperature drop across the orifice plate is about one-fourth of the temperature in degrees Fahrenheit of the molten metal in the reservoir above its solidification temperature.

lf the cold shutting occurs most heavily in only one section of the cast ingot, with the surface of the remainder of the ingot being satisfactory for the uses to which the ingot will be put, then the heat conductive segment need only be positioned to retard solidification of the embryo shell of metal adjacent to the section of the orifice plate corresponding to the section where the undesired cold shutting is occurring. Usually, it is preferred that the outer edge of the heat conductive segment extend outwardly at least as far as about the perimeter of the mold hollow. This will insure the retardation of solidification at the perimeter adjacent to the orifice plate which seems to be the cause of most of the trouble. In horizontal continuous casting apparatus, it is frequently found that only the lower surface of the ingot has cold shutting to such an extent to be unacceptable, while the upper surface of the ingot is satisfactory although perhaps not completely free of cold shuts. In this situation the heat conductive segment need only form the lower half of the orifice plate and extend outwardly at least as far as about the perimeter of the mold hollow. In other circumstances, it may be desirable to form the entire portion of the orifice plate within the perimeter of the mold hollow of the heat conductive material. In this case the entire central portion of the orifice plate within the perimeter of the mold hollow is, of course, the heat conductive segment.

Although not essential to the practice of the instant invention, it is found as a practical matter that the orifice plate and its heat conductive segment should be of a material that is substantially nonwctting with respect to the molten metal being cast. This prevents adherence of metal to the orifice plate at the commencement of casting and at any time during the casting operation when something should cause metal to solidify contiguous to the orifice plate. The most important consideration is that there be a segment in the orifice plate of a heat conductive material. For present purposes, a heat conductive material is defined as a material having a thermal conductivity (K factor) at 32-2l2F. of at least about 45 B.t.u./(hr.) (sq. ft.) (F.)/(ft.). Among those materials which could advantageously be used are iron and steel alloys having a K factor above 45 if provided with a coating of aluminum oxide or other suitable material nonwetting with respect to the metal being cast. The aluminum oxide coating is particularly efficacious, of course, if aluminum is being cast. Boron nitride bonded titanium diboride is also a suitable material. Those materials known as refractory hard metals, if provided with a suitable nonwetting coating can also be utilized. In some cases, the insert in the orifice plate may have to be preheated to prevent spalling, depending upon the characteristics of the materials. It has been found that graphite seems to be the optimum material for the heat conductive segment. Graphite is nonwetting with respect to most metals being cast. Normally, for the size molds used in continuous casting, no preheating of the graphite is necessary. Graphite will normally have a K factor, as defined above, in a range from 70-90. K factors may be converted to metric units, cal./(sec.) (cm) (C.)/(cm.) by multiplying the English unit K factor by 0.00413.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view, partly in section, of a continuous casting apparatus embodying the principles of the instant invention.

FIG. 2 is a front plan view of the orifice plate used in the apparatus shown in FIG. 1.

FIG. 3 is a front plan view of another orifice plate embodying the principles of the instant invention.

FIG. 4 is a front plan view of another orifice plate embodying the principles of the instant invention.

FIG. 5 is another front plan view of an orifice plate embodying the principles of the instant invention.

DETAILED DESCRIPTION With reference now to the drawings wherein like numerals have been used to represent like parts, it will be seen that FIG. 1 illustrates a continuous casting apparatus embodying the principles of the instant invention. In FIG. 1, a chilled metal mold is generally designated 10. It is separated from reservoir 12 containing molten metal 14 by orifice plate assembly 16.

The orifice plate, also shown in FIG. 2, has at least one passageway 18 therein for fiow of molten metal 14 from reservoir 12 into mold I0. As shown here, a plurality of passageways 18 are evenly distributed around the surface of the orifice plate close to the perimeter thereof. This is a preferred arrangement for continuous casting but is not essential to the practice of the instant invention. Various other passageway arrangements such as elongated slots of various shape, single wide holes, and various combinations are known to those skilled in the art and all may be equally used in the practice of the instant invention. As shown, orifice plate 16 has a substantially heat conductive segment 20 positioned therein. The orifice plate itself is made of a heat insulating material, i.e., a material having a K factor less than 45 as defined above. A suitable material for orifice plate 16 is that known in the trade as marinite. Marinite is a mixture of asbestos fibers and diatomaceous earth. It is a good insulator, nonwetted by molten aluminum and not subject to significant attack by molten aluminum. As has been discussed hereinabove, a suitable material for heat conductive segment 20 is graphite. A simple but effective way to insert the heat conductive segment 20 into the orifice plate 16 is by that technique known as press fitting. As shown in the drawings, chilled mold 10 includes a cooling water jacket 22 having a water inlet 24 therein. Appropriate nozzles permit the passage of cooling water from the water jacket in the form of sprays through the mold l0 and against the ingot 28 emerging from the mold assembly, thereby cooling it.

Reservoir I2 is desirably made with thick heat insulating refractory walls that are impervious to molten metal and poor conductors of heat in order to maintain the temperature of the molten metal 14 contained therein substantially constant. In the embodiment shown in FIG. I, orifice plate 16 is separated from chilled mold 10 by a heat insulating gasket 30. The gasket 30 is preferably a material with very low-heat conductivity so that a large temperature gradient can exist across its thickness. Gasket 30 may be of such material as asbestos and it may be an element of a lubrication system, for example, by having channels 32 cut in the face in contact with chill mold 10. An oil reservoir 34 fillable via oil inlet 36 is attached to chilled mold 10. Oil passes from oil reservoir 34 via channels 32 by capillary action in the embodiment shown; or by pressure in other systems, so that a stream of lubricant is directed into the hollow of chilled mold I0 and forms part of the heat insulating section and thermally insulates the heat conductive segment 20 from chilled mold 10.

'As has been discussed, various shapes for the heat conductive segment 20 are possible. In the apparatus shown in FIGS. I and 2 the heat conductive segment occupies the entire inner area of orifice plate 16 and extends outwardly to about the perimeter of the hollow of chilled mold 10. In the embodiment shown in FIG. 3, a smaller heat conductive segment 20 is used. This would be used when the undesirable cold shutting is confined to only a relatively small area of the ingot surface. Similarly, in the embodiment shown in FIG. 4, the heat conductive segment 20 forms the lower half of the orifice plate 16 and extends outwardly to about the perimeter of the mold hollow. It may, of course, extend beyond the mold hollow but there normally is no technical advantage to doing so unless it should become necessary to rebore the mold hollow.

In the embodiment shown in FIG. 5, the heat conductive segment 20 is in the form of a concentric ring in orifice plate 16, again with its outer edge extending to substantially the perimeter of the hollow of mold 10.

A series of tests were used to evaluate the instant invention.

In all cases, apparatus similar to that shown in FIGS. 1 and 2 was utilized. As a heat insulating lubricant, in these tests, a mineral oil known in the trade as Nopcorol XS-3 was used as the heat insulative lubricant. Nopcorol XS-3 is a mineral oil with the characteristics of BW 38 sperm oil. Another suitable (u Si .\l z Zn Ti Ni Al 2. 2H ll. 13 1.21 1.4" u. U6 1.112 Balance.

1 Maximum ".25.

The metal was stirred, chlorine fluxed until the vacuum freeze test showed zero bubbles, and then held at 1,300F. for easting. Three casts of 3-inch diameter ingot were made of 2618 alloy with a lubricant flow rate at the top of the mold of0.00- 0.25 and at the bottom of 0.l-0.50 milliliters of lubricant per minute. The casting rate was 12 inches per minute and the flow rate of coolant water was 60 gallons per minute. The first cast of this alloy was considered exploratory. The ingot displayed a heavy top oil stripe throughout the cast with surface folds that were heavier on the sides than on the top. The oil stripe was due to difficulties with the control system for the lubricant. Accordingly, another cast under conditions similar to those in the above discussed cast and of the same alloy was made. The only difference here was that the casting rate was reduced slightly to l 1% inches per minute. Both top and bottom surfaces of the ingot were heavily and nonuniformly cold folded. in the next cast a heat conductive segment similar to that shown in FIGS. 1 and 2 was positioned in the orifice plate. The casting rate was increased to l2 inches per minute. The same alloy was cast and the other conditions were the same. The ingots cast surface was lightly and uniformly cold folded, to a much lesser degree than the previous casting. Approximately 600 lbs. of metal were cast in this casting. It is believed that this improved surface condition was because the heat conductive insert retarded solidification of the surface zone or embryo shell of the ingot adjacent to the orifice plate and permitted solidification to occur further away from the mold entry and at a rate substantially equal to that of the ingot withdrawal.

The next test involved the horizontal continuous casting of 4%-inch diameter l(A-08 aluminum alloy.

KA-OS Composition [Percent by weight] Cu Mu Others cach=320 maximum; Others t0tal=.80.

F@ g i- .n. airnu 1 H. Again, the equipment was similar to that shown in FIGS. 1 and 2 although a larger capacity furnace feed was utilized. The furnace feed averaged 30,000 lbs. capacity.

The initial casts made with an all marinite orifice plate repeatedly displayed surface pitting or worm holes regardless of molten metal or lubricant distribution patterns. Variations in melt temperatures and casting rates were to no avail. When chemical compositions were maintained within the limit believed necessary in order to cast acceptable ingot, surface pitting or worm holes persisted. These results are believed to lend further support to the theory that cold shuts are, at least in part, a phenomena occurring at the junction line of the mold and orifice plate. A surface pit is believed to be the void left when rapidly cooling molten metal flowing circumferentially around the junction line loses its fluidity before completing a full 360 encompassment of the junction line area. A surface pit is in effect the start of a cold fold. This becomes quite clear when, as casting rates are decreased, there is a corresponding increase in both the numbers and the severity of the pitting or worm holes. Still further slowing of the casting rate results in merging ofthe pits into unacceptable circumferential continuous cold folds.

In accordance with the instant invention, this condition can be eliminated by maintaining metal temperatures sufficiently high to assure metal fluidity at the junction line. Accordingly, an orifice plate containing agraphite heat conductor insert ex- Zn Al .03 Balance posed to the superheat of the incoming molten metal stream and of the type shown in FIGS. 1 and 2 was fabricated and positioned in the casting assembly. Under this condition the mold produced acceptable ingots. in all cases the casting rates were limited to 22-23 inches per minute.

it is believed that the above examples illustrate the principles of the invention and show the adlvantageous results of the use thereof. The formation of cold folds, worm holes, rebleeds, and other types of cold shuts are minimized in that the instant invention provides a superheated mold closure that retards the upward solidification of the embryo shell adjacent the orifice plate. The superheat of the incoming molten alloy on both sides of the orifice plate is sufficient to maintain the heat conductive insert temperature'above the melting point of the alloy being cast. Molten metal passing through the orifices of the orifice plate retain sufficient heat upon arrival at the mold wall-orifice plate junction line to prevent solidification of the embryo shell to occur at a rate greater than that of ingot withdrawal. As a result the forming ingot has a completely molten metal top to the full diameter of the mold bore. The ingot embryo shell then builds up or is supplied from a molten metal meniscus source rather than from a meniscus source that is alternately solid and liquid.

There are alternate constructions of the apparatus not discussed in detail herein which are also within the scope of the instant invention. For example, the heat conductive insert can be discontinuous, that is in the form of a series of plugs passing through the orifice plate from one face to the other. This form of orifice plate assembly is particularly desirable when the heat conducting element is metallic and it is desired to put a protective coating on those portions that would normally be in contact with molten metal. Heat conductive segments in any form that provide a heat conductive pass from the metal in the reservoir to the metal in the immediate vicinity of the meniscus in the mold will produce beneficial results in accordance with this invention although not necessarily all to the same degree.

Although the a aratus of thismamas'rsgaasfiiyisau i for horizontal continuous casting, it may also be useful for vertical continuous casting, particularly, when casting large cross section ingots, ingots withcomplex cross-sectional shapes, i.e. other than circular, and ingots of metal that must be cast slowly. Thus, while there have been shown and described hereinabove possible embodiments of the invention, it is to be understood that the invention is not limited thereto and that various changes, alterations, and modifications can be made thereto without departing from the spirit and scope thereof as defined in the appended claims wherein:

Iclaim:

1. Apparatus for the continuous casting of molten metal which comprises:

a. a hollow chilled mold assembly;

b. a reservoir for molten metal;

c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and

d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material and being so proportioned that the temperature drop across the orifice plate is not more than about one-half of .the temperature in F of the molten metal in the reservoir above its solidification temperature.

2. Apparatus for the continuous casting of molten metal which comprises:

a. a hollow chilled mold assembly;

b. a reservoir for molten metal;

c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and

d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast inthe mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material and being so proportioned that the temperature drop across the orifice plate is'about onefourth of the temperature in degrees Fahrenheit of the molten metal in the reservoir above its solidification temperature.

3. Apparatus for the continuous casting of molten metal which comprises:

a. a hollow chilled mold assembly;

b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having. a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and

d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material having a thermal conductivity at 32 212F ofat least about 45 B.t.u./(hr.)(sq.ft.) (F.) (ft.).

4. The apparatus of claim 3 wherein a stream of lubricant thermally insulates the heat conductive segment from the chilled mold.

5. The apparatus of claim 3 wherein the outer edge of the heat conductive segment extends outwardly at least as far as about the perimeter of the mold hollow.

6. The apparatus of claim 3 wherein the heat conductive segment forms the lower half of the orifice plate extending outwardly a least as far as the perimeter of the mold hollow.

7. The apparatus of claim 3 wherein the heat conductive segment forms the portion of the orifice plate within the perimeter of the mold hollow.

8. The apparatus of claim 3 wherein the mold is disposed in a horizontal position for horizontal continuous casting.

9. The apparatus of claim 3 wherein heat-insulating means including a gasket element are provided for spacing the heat conductive segment from the mold assembly.

10. Apparatus for the continuous casting of molten metal which comprises:

a. a hollow chilled mold assembly;

b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and

d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of graphite. 

1. Apparatus for the continuous casting of molten metal which comprises: a. a hollow chilled mold assembly; b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material and being so proportioned that the temperature drop across the orifice plate is not more than about one-half of the temperature in *F of the molten metal in the reservoir above its solidification temperature.
 2. Apparatus for the continuous casting of molten metal which comprises: a. a hollow chilled mold assembly; b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material and being so proportioned that the temperature drop across the orifice plate is about one-fourth of the temperature in degrees Fahrenheit of the molten metal in the reservoir above its solidification temperature.
 3. Apparatus for the continuous casting of molten metal which comprises: a. a hollow chilled mold assembly; b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of a material having a thermal conductivity at 32*-212*F of at least about 45 B.t.u./(hr.)(sq.ft.) (*F.) / (ft.).
 4. The apparatus of claim 3 wherein a stream of lubricant thermally insulates the heat conductive segment from the chilled mold.
 5. The apparatus of claim 3 wherein the outer edge of the heat conductive segment extends outwardly at least as far as about the perimeter of the mold hollow.
 6. The apparatus of claim 3 wherein the heat conductive segment forms the lower half of the orifice plate extending outwardly a least as far as the perimeter of the mold hollow.
 7. The apparatus of claim 3 wherein the heat conductive segment forms the portion of the orifice plate within the perimeter of the mold hollow.
 8. The apparatus of claim 3 wherein the mold is disposed in a horizontal position for horizontal continuous casting.
 9. The apparatus of claim 3 wherein heat-insulating means including a gasket element are provided for spacing the heat conductive segment from the mold assembly.
 10. Apparatus for the continuous casting of molten metal which comprises: a. a hollow chilled mold assembly; b. a reservoir for molten metal; c. an orifice plate made of a heat-insulating material and having a perimeter at least equal to the perimeter of the hollow portion of the mold assembly and positioned between and contiguous both to the mold assembly and the reservoir, said plate also having a passageway therethrough for transferring molten metal from the reservoir into the hollow portion of the mold assembly; and d. a substantially heat conductive segment mounted in the orifice plate and so oriented relative thereto as to be spaced from the mold assembly so that it can effect transfer of heat therethrough from the reservoir into the hollow portion of the mold assembly adjacent to the orifice plate while avoiding transfer of heat to the mold assembly, whereby solidification of the embryo shell of metal being cast in the mold assembly adjacent to the orifice plate is retarded and the formation of cold shuts in the metal is reduced, said heat conductive segment being made of graphite. 